1. Field
This invention is in the general field of dispensing apparatus and specifically valves made of flexible material and operated by flexing of the material; i.e. squeezing the valve. More specifically it is in the field of such valves which can be located at the outflow end of a conduit so that when the valve is closed and the flow stopped there is a minimum of residual flow.
2. Prior Art
The prior art to the subject invention is the valve disclosed in U.S. Pat. No. 4,690,375. That valve comprises a hollow elastomeric body having an inlet and an outlet and, in the preferred embodiment, one wafer-like part fitted into the hollow interior of the body. The shapes of the interior of the body and the wafer-like part are such that when the valve is at rest the wafer blocks flow from the inlet to the outlet. When the body is distorted by finger pressure the wafer-like part, termed the wafer for purposes of this disclosure, also is distorted and a passage is opened, permitting flow through the valve. The body of the valve and the cavity in it are essentially elliptical in side (elevational) view and in cross section. The distortion forces are applied at the ends or the cross sectional ellipse midway between the inlet and outlet. The distortion tends to transform the cross sectional shape from essentially elliptical towards circular.
In the continued development and use of the valve disclosed in the above mentioned patent certain problems have become evident, the solutions for which constitute improvements in the basic valve. One problem was that too much finger pressure was needed to distort the valve. The second was that increased pressure against sealing surfaces tended to force the sealing surfaces apart, allowing leakage, rather than force the surfaces together in a positive seal.
The third problem faced was one of part cost. Solvent-resistant elastomeric wafer materials, necessary for the gasoline-dispensing application described in the prior art, of the requisite softness are typically molded in a relatively time-consuming and expensive thermoset molding and vulcanizing process rather than the less expensive thermoplastic injection molding process. Use of certain closed-cell foams allows use of harder, more solvent-resistant base polymers while, because of the entrained air in the foam, providing the necessary flexible and conforming properties for a effective seal. Simple closed-cell foam parts can be thermal/pressure formed out of sheet stock, and are much less expensive to form per part than thermoset-molded/vulcanized parts. The objectives of the invention are to make the valve easier to distort (open), to cause the sealing surfaces to seal more tightly with increased pressure, while reducing total cost of the valve.